Težave z ravnotežjem sodijo med pogoste vzroke za obisk pri zdravniku, njihov izvor pa je lahko precej raznovrsten. Na področju otorinolaringologije se posvečamo predvsem okvaram notranjega ušesa in ...ravnotežnega živca ter nakažemo morebitno centralno prizadetost ravnotežnega sistema. Za postavitev diagnoze pogosto ne zadostuje zgolj ena preiskava, pač pa je po navadi potrebna kombinacija različnih testov, s katerimi potrjujemo ali izključujemo prizadetost posameznih delov ravnotežnega sistema. V osnovi razlikujemo med testi, s katerimi ocenjujemo delovanje polkrožnih kanalčkov, in testi za oceno delovanja sakulusa in utrikulusa. Predstavljena je klinična raziskava, v kateri smo pri 1.042 bolnikih z jasno anamnezo za benigni paroksizmalni pozicijski vertigo le-tega dokazali v 36 %. Nujno je bilo opraviti še dodatna testiranja, ki jih predstavlja prispevek. Za razlago njihovih rezultatov se pogosto zanašamo na opazovanje in merjenje gibanja očesnih zrkel, pri čemer je pomembno poznavanje določenih refleksov za ohranjanje ravnotežja. Ob tem moramo upoštevati tudi simptome, ki jih navaja bolnik, in teste po potrebi dopolniti s slikovnodiagnostičnimi preiskavami. Natančne računalniške meritve in grafični zapisi danes nadomeščajo opazovanje s prostim očesom in subjektivno razlaganje opažanj preiskovalca.
The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: ...soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.
A drop calorimetry method was used to measure the partial and integral mixing enthalpies of Ag-Mg-Pd liquid solutions. The experiments were performed for six separate series of liquid alloys starting ...from the binary alloys with constant xAg/xMg ratios equal to 1/9, 1/3, 1/1, and 3/1 for (Ag0.10Mg0.90)1-xPdx and (Ag0.25Mg0.75)1-xPdx at 1116 K and (Ag0.50Mg0.50)1-xPdx and (Ag0.75Mg0.25)1-xPdx at 1279 K and xMg/xPd ratios of 9/1 and 4/1 for (Mg0.90Pd0.10)1-xAgx and (Mg0.80Pd0.20)1-xAgx at 1116 K. Then, using the thermodynamic properties of the binary systems in the form of the Redlich-Kister equations and the changes in mixing enthalpies provided by this study, the ternary interaction parameters were determined with the Muggianu model and our own software (TerGexHm). Based on the binary and ternary interaction parameters, the partial mixing enthalpies of Ag, Mg, and Pd were calculated for the same cross-sections where the measurements were conducted. These studies were the first step of an investigation of the Ag-Mg-Pd system before the calculation of the phase diagram for this ternary system.
The limiting enthalpy of the solution of liquid indium in liquid tin was measured at 723 K. The calorimetric method was applied to determine the standard enthalpy of the formation of intermetallic ...phases and alloys from the In-Li system. The measurements were done at 747 K and 756 K. The structures of prepared alloys were confirmed by the X-ray diffraction measurements. Besides that, the ab initio calculations allowed the modeling of the formation energies, the volume thermal expansion, the heat capacity under constant pressure, and the elastic properties of the intermetallic phases. The theoretical formation energies show good agreement with the experimental findings. The analysis of the phonon dispersion indicates an instability of the InLi phase in the Fd-3m space group. A further investigation on the atomic arrangement in the case of the equiatomic ratio is suggested.
Reakcijska kalorimetrija Horvat, Gordan
Kemija u industriji,
11/2015, Letnik:
64, Številka:
11-12
Journal Article, Paper
Recenzirano
Odprti dostop
U radu je dan sažet prikaz principa rada reakcijskih kalorimetara. Opisani su adijabatski kalorimetri te kalorimetri kondukcijskog i kompenzacijskog tipa. Uz kalorimetre zatvorenog tipa opisani su i ...kalorimetri perfuzijskog tipa. Iznesena je fizikalna osnovica načina mjerenja topline za svaki od navedenih tipova kalorimetara. Također su navedeni postupci kalibracije kalorimetara.
The aim of the study is to show the differences between the measured and estimated values of resting energy expenditure and any changes occurring after the 6-month weight loss intervention program.
...We included 33 healthy adults aged 25-49 years with an average body mass index 29.1±2.7 kg/m 2 for female and 29.8±2.8 kg/m
for male. The measured resting energy expenditure was obtained by indirect calorimeter MedGem® Microlife and estimated resting energy expenditure by the Harris-Benedict equation, the Mifflin-St Jeor equation, the Owen equation, the Wright equation, and by the Tanita body composition analyser. All measurements and calculations were carried out before and after the 6-month intervention. Results were compared using paired t-tests. P value less than 0.05 was considered statistically significant.
A comparison of the measured resting energy expenditure of female subjects with the estimated resting energy expenditure using the Harris-Benedict equation, the Mifflin-St Jeor equation and the Wright equation showed a statistically significant difference. A comparison of the measured resting energy expenditure of male subjects with the estimated resting energy expenditure using the Harris-Benedict equation and the Wright equation showed a statistically significant difference. There was a significant difference in the measured resting energy expenditure and estimated resting energy expenditure using Tanita.
We concluded that the most comparable equation for our sample was the Owen's equation. After losing weight, the measured resting energy expenditure has decreased, which must be taken into account in further diet therapy.
U ovom radu istražena je kinetika izotermne kristalizacije i kristalna struktura mješavina termoplastičnog poliuretana i polipropilena (TPU/PP) te termoplastičnog poliuretana i polipropilena uz ...dodatak talka (TPU/PP/T) različitog sastava (80/20, 50/50 i 20/80) diferencijalnom pretražnom kalorimetrijom (DSC). Kristalizacija je proučavana u području temperatura od 116 °C do 132 °C. Ustanovljeno je da je kristalizacija brža za mješavine TPU/PP/T. Kinetika izotermne kristalizacije opisana je pomoću Avramijeve jednadžbe. Utjecaj različite izotermne temperature proučavan je usporedbom vrijednosti kinetičkih parametara kao što su Avramijev eksponent, n, kinetička konstanta brzine kristalizacije, k, i polovično vrijeme kristalizacije, t1/2. Dobiveno je da se Avramijev eksponent kreće u rasponu od 1,18 do 2,31. Ti rezultati ukazuju na dvodimenzijski rast kristalnih jedinica.
Kinetika izotermne kristalizacije pokazala je da se dodatkom talka povećava kristalište i raste konstanta brzine kristalizacije, k, mješavina TPU/PP. Za dane temperature kristalizacije, polovično vrijeme kristalizacije, t1/2, mješavina TPU/PP/T niže je od pripadajućih vrijednosti kod mješavina TPU/PP.
Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna .
A mixture of phosphoric and sulfuric acid was used to investigate the dissolution kinetics of phosphate ore by Differential Reaction Calorimetry (DRC). The effect of the solid-to-iquid ratio, ...concentration, stirring speed, particle size and temperature of the reaction is examined. It was established that the dissolution rate increased with stirring speed and particle size. However, rising the olid-to-iquid ratio, temperature and concentration decreased the dissolution rate. It was determined that the dissolution rate fits in the first order of the pseudo-homogeneous reaction model. Two negative values of apparent activation energies were found in the range of 25 to 60?C. The experimental data were tested by graphical and statistical methods and it was found that the following models were best fitted for the experimental data and an empirical equation for the process was developed. -ln (1 ? x) = 2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (2671/T)t. T? 40?C -ln (1 ? x) = 2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (6959/T)t. T > 45?C
nema
Identification and characterization of different forms of methotrexate were carried out by crystallization from different solvents. Five different forms of the drug were obtained. Appearance of a ...desolvation endotherm in the DSC accompanied by mass loss in TGA for forms I, II, IV and V showed these forms to be acetonitrile solvate hydrate (form I), trihydrate (forms II and IV) and dimethylformamide solvate (form V), respectively. However, the desolvation peak was absent in form III (obtained from methanol) indicating the absence of any solvent of crystallization. This form was found to be partially crystalline by its XRPD pattern. Solution calorimetry was further used to differentiate between the forms as they differ in lattice energy, resulting in different enthalpies of solution. The dissolution and solubility profiles were correlated with the enthalpy of solution and subsequently with crystallinity of all the forms; the least endothermic form (form III) had the highest dissolution rate.
U radu je provedena identifikacija i karakterizacija pet različitih formi metotreksata dobivenih kristalizacijom iz različitih otapala. Desolvatacijska izoterma u DSC popraćena gubitkom mase u TGA za forme I, II, IV i V ukazuje da su te forme solvati s acetonitrilom: hidrat (forma I), trihidrat (forma II i IV) i solvat s dimetilformamidom (forma V). Međutim, desolvatacijski pik je odsutan u formi III (dobivenoj iz metanola) što ukazuje na odsutnost otapala u kristalnoj formi. Ta forma je parcijalno kristalna i pokazuje odgovarajući XRPD uzorak. Energija kristalne ćelije je za različite forme različita, što ima za posljedicu različite entalpije otapanja te omogućava primjenu kalorimetrije otopine za diferencijaciju formi. Topljivost je korelirana s entalpijom otopine i kristaliničnosti svih formi. Najmanje endotermna forma (forma III) je najbolje topljiva.
Oksidacija masti je jedna od osnovnih reakcija koja utječe na pad
kvalitete maslaca i masla kako s gledišta proizvođača tako i s gledišta potrošača navedenih proizvoda, kao i proizvoda s njihovim ...sadržajem. Obzirom da je većina produkata reakcije oksidacije masti štetna po zdravlje potrošača, nedovoljno praćenje kvalitete jestivih masti i proizvoda koji ih sadrže dovelo bi do rizika po zdravlje potrošača, a i do financijskih gubitaka proizvođača. Pri procjeni oksidacione stabilnosti masti do danas su korištene standardne kemijske metode, odnosno određivanje karakterističnih brojeva (jodni, kiselinski, peroksidni, anisidni itd.) čiji proces zahtijeva upotrebukemikalija i dugo traje. Međutim analiza pomoću diferencijalne skenirajuće kalorimetrije (DSC) pokazuje da se jednostavnim načinom u vrlo kratkom vremenu, može utvrditi oksidaciona stabilnost maslaca i masla. Provedena su laboratorijska istraživanja mogućnosti primjene diferencijalne skenirajuće kalorimetrije (DSC) pri praćenju oksidacione stabilnosti maslaca i masla, kako u svježem stanju tako i već upotrijebljenom za prženje. Dobiveni rezultati komparirani su s promjenom jodnog broja određenog standardnom metodom. Postignuti rezultati potvrđuju opravdanost i mogućnost primjene diferencijalne skenirajuće kalorimetrije pri praćenju oksidacione stabilnosti maslaca i masla.